Salt effect on gas dispersion in flotation column – Bubble size as a function of turbulent intensity

The present work investigates the role of chloride salts on bubble coalescence properties by average bubble diameter measurement. The tested chloride salts (NaCl, MgCl₂ and CaCl₂) were dissolved in fresh running water and used as feeding of a three-meter high pilot flotation column. The column was operated in close circuit while the superficial gas rate (J_g) was varied. Gas holdup in the collection zone of the column was measured using pressure sensors. Drift flux model is employed to obtain the mean bubble diameter between two pressure-tapping points. The change of cations of chloride salts has an indisputable effect on bubble coalescence; hence the bubble size in the column varies as a function of chloride salt type. The hydrodynamics factors on bubble coalescence and difference in inhibition behavior of monovalent (NaCl) and divalent cations (CaCl₂ and MgCl₂) based on the partition of the different hydrated ions at the gas-liquid interface were highlighted. The characterisation of the liquid phase used for flotation separation should not only focus on the concentration of salts but also on the ion-water, ion-ion and water-water properties as a function of hydrodynamic condition.